The knowledge that can be acquired concerning various petrophysical parameters of rocks during drainage or imbibition phases can be used, for example, for selecting the most appropriate fluid for displacing the petroleum hydrocarbons, the works contain and for improving thereby the efficiency of oil enhanced recovery processes in a reservoir.
It is known to determine, for example, the saturation and the wettability of rocks with respect to fluids such as the water (in the form of brine) and the oil that can be contained therein. To that effect, rock drainage phases are carried out, i.e. a displacement of the fluids intended to decrease the water saturation, followed by imbibition phases which, on the contrary, are intended to increase its water saturation (Sw). Devices for measuring petrophysical parameters of rocks are described, for example, in patent applications FR-2,603,040, EN-93/09,481 or EN-94/10,783 or in U.S. Pat. Nos. 4,868,751 or 5,069,065.
In order to measure the capillary pressure at a point of a porous sample in the presence of two fluids in the continuous phase (water and oil for example), that is defined as the difference Pc at equilibrium between the pressure P(oil) and the pressure P(water), one has to be able to measure these two pressures separately. Existing pressure taps do not allow selective pressure tappings to be performed in a dynamic flow of two fluids.